Chapter 19 — Chemical Coordination and Integration

Chemical coordination in the human body is carried out by hormones, non-nutrient chemicals produced by endocrine glands and other tissues that act as intercellular messengers, working alongside the neural system to regulate physiological functions including metabolism, growth, development, and homeostasis.

Chapter 19 covers the endocrine system and chemical coordination in humans. The chapter explains how hormones—produced by glands like the hypothalamus, pituitary, thyroid, parathyroid, pancreas, adrenal, thymus, and gonads—regulate metabolism, growth, and development. Key topics include the structure and functions of major endocrine glands (hypothalamus regulates pituitary; thyroid hormones control metabolic rate; pancreatic insulin and glucagon maintain blood glucose; adrenal catecholamines trigger fight-or-flight responses), hormone mechanisms of action via receptors, and non-endocrine hormone sources (heart, kidney, gastrointestinal tract). The chapter also addresses hormonal disorders like diabetes mellitus, hypothyroidism, and Addison's disease.

1. 01The endocrine system comprises organized glands (pituitary, thyroid, adrenal, pancreas, parathyroid, thymus, pineal, gonads) plus hormone-secreting cells in the heart, kidney, and gastrointestinal tract
2. 02The hypothalamus regulates the pituitary through releasing and inhibiting hormones via a portal circulatory system, controlling anterior pituitary; the posterior pituitary is under direct neural regulation
3. 03Thyroid hormones (T3, T4) regulate basal metabolic rate, carbohydrate/protein/fat metabolism, and require iodine; deficiency causes hypothyroidism (goitre, cretinism); excess causes hyperthyroidism (Graves' disease)
4. 04Pancreatic insulin (β-cells) decreases blood glucose by promoting uptake and glycogenesis, while glucagon (α-cells) increases blood glucose via glycogenolysis and gluconeogenesis; imbalance causes diabetes mellitus
5. 05Adrenal catecholamines (epinephrine, norepinephrine) trigger fight-or-flight responses increasing heart rate, respiration, and glucose availability; cortical glucocorticoids regulate metabolism and immunity, mineralocorticoids control electrolyte balance
6. 06Hormone action occurs via two pathways: membrane-bound receptors generate second messengers (cAMP, IP3, Ca²⁺) for protein hormones; intracellular receptors regulate gene expression for steroids and thyroid hormones